Underfed stoker



J. A. CASEY 2,365,679

- UNDERFED STOKER v Filei Nov. 25, 1941 3 Sheets-Sheet 1 J. A, CASEYUNDERFED STOKER Dec, 26, 1944,

3 Sheets -Sheet 2 I Filed Nov. 25, 1941 Dec. 26, 1944. J. A. CASEYUNDERFED STOKER Filed Nov. 25, 1941 3 Sheets-Sheet 3 Patented Dec. 26,1944 UNITED STATES PATENT OFFICE UNDERFED STOKER James A. Casey,Wilkes-Barre, Pa.

Application November 25, 1941, Serial No. 420,413

Claims.

This invention relates to automatic coal stokers of the type havin anunderfed burner comprising' an inverted frusto-conical casing defining afuel chamber and surrounded by a jacket in communication with theconduit of a blower, the easing having circumferential narrow louvers atdifferent levels for admitting air from said jacket into the fuel massin said fuel chamber. Said burner is, of course, in a combustion chamberwhich communicates with a chimney.

Coal is fed from a, bin, hopper or other form of coal supply, to thelower part of the burner by a conveyor in a coal tube; the coalparticles being generall of small size and accompanied by considerabledust. A layer of ashes of varying. thickness may overlie the combustionbed in the fuel chamber and constitutes more or less of an obstructionthrough which the air entering through the louvers must be forced.

As heretofore constructed, such stokers have certain drawbacks inoperation. The layer of ash may sometimes create back pressure, causingthe forced draft to blow the products of combustionback through the coaltube into the bin.

hopper or coal box as the case may be, letting the gas and coal dustescape into the building.

The coal dust carried into the burner with the coal may not only clogthe interstices in the fuel mass, but may stop up more or less of the cthe burner and coal box, to prevent the back travel of gas from theburner to the anterior part of the coal feeding system.

A further object of the invention is to provide a coal box intermediatethe bin and coal tube,

the atmosphere of which is evacuated into the combustion chamberadjacent the burner, and to provide for a cascade of the coal columnmov-- ing from bin to burner, within said coal box, whereby the dust isseparated from the larger coal particles, drawn on with the atmosphereof the coal box into the combustion chamber and ignited by the name fromthe burner.

Still another object of the invention is the.

formation of a coal seal at the point where the feed conveyor from thebins enters the coal box,

for the purpose of holding the vacuum in the coal box which isessential'to the withdrawal of the dust.

Another object of the invention is to provide a pulverizer in the lineof the feed conveyor from bin to coal box for reducing the coal touniform small size. and producing a quantity of dust auxiliary to thatwhich incidentally accompanies the coal, so asto have sufficient dust tomaintain lively incandescent combustion in the combustion chamberadjacent the burner.

A further object of the invention is to provide conveyors of varyingpitch and diameter in their different zones of travel in both the feedtube from bin to coal box and the coal tube from coal box toburnenforproducing optimum conditions of flow, density and fullness in differentparts of the coal tubes, as will appear.

A still further object of the invention is to provide a 'novelconstruction of conveyor end portion and the adjacent casing portionwithin the bin, enabling the conveyor to pick up coal from an extensivearea of the coal pile within the bin. I

Another object of the invention is the novel combination of stoker airfeed and the boiler served by said stoker wherein the air is preheatedby products of combustion on their way to the stack through the gaspassages of the boiler.

Another object of the invention relates to the j provision of variousmeans for evacuating thev coal box.

Other objects of the inventionwill appear as the following descriptionof a preferred and practical embodiment thereof proceeds:

In the drawings which accompany and form a part of the followingspecification and throughout the several figures of which the same char:acters of reference have been employed to designate identical partsz YFigure 1 is a side view, partly in section, of a stoker mechanismembodying the principles of the present invention;

. Figure 2 is a longitudinal section, on an -enlarged scale, of the coaltube and conveyor extending from bin to coal box;

Figure 3 is a cross-section taken along the line 3-3 of Figure 2;

Figure 4 is a cross-section taken along the line 4-4 of Figure 2;

Figure 5 is a plan view, partly in section, showing an air system forevacuating the coal box, in which an auxiliary fan is employed;

,Figure 6 is a similar view of a modified form in which the naturalstack draft is used;

Figure '7 is a side elevation, partly in section, showing a form of theinvention in which the main blower produces a draft on the coal boxj 1Figure 8 is a side view, partly in vertical section, showing means forpreheating the air to the stoker through heat interchange with theproducts of combustion passing through a boiler and to the stack;

Figure 9 is a similar view illustrating a modified form of theinvention.

' Referring now in detail to the several figures,

and first adverting to Figures 1 to 4, inclusive, the numeral lrepresents in general a coal stoker having th chassis 2 which supports,on the one hand a burner 3, and onthe other the coal box I and blower 5.The burner 3 is located in a combustion chamber 6, a wall of which isshown at 1. To the left of the coal box as shown, is a bin 8.

A coal tub 9 with an enclosed coal conveyor l0 extends from within thebin 8 to the. coal box 4. A coal tube H with enclosed coal conveyor l2,extends'from the coal box 4 to the burner. The

' which is underfed from the coal tube II, the

ashes developing toward the top of the burner and being dislodged bymeans such as the rotary arm l9 which travels around the lip 20, formingthe upper periphery of the burner.

The coal tube I I is surrounded by an air conduit 2| in communicationwith the pressure end of the blower 5, the induction end of which bloweris open to atmosphere. The end of the air conduit 2| adjacent the burneris an upturned elbow 22, upon which rests an air Jacket 23, the chamberof which communicates with the fuel chamber of the burner through thelouvers l8.

So much of the structure as has thus. far been described is present inknown stokers.

The operation of such a stoker is attended by certain drawbacks. Forinstance, after long periods of slow combustion an ash mass may collecton top of the burner, which constitutes a material obstruction to thepassage of air through the fuel bed. The result may be a development ofback pressure in which products of combustion are forced back throughthe coal tube l I, escaping from the coal box or traveling through thecoal tube to the bin, in either case, escaping into the building.

Inasmuch as the small sized coal generally employed in domestic stokersis accompanied by a considerable proportion of coal dust, the latter mayclog the interstices between the coal particles in the fuel bed and mayalso more or less stop the burner.

.efliciency of the stoker plate by maintaining a lively incandescentcombustion in the combustion chamber in the region of the top. of theburner. The reference character 24 designates a vent communicating atone end with the coal tube H adjacent the burner and opening into thecombustion chamber 6. This vent short-circuits any gas back pressurefrom the burner into the coal tube and. delivers the gases into thecombustion chamber where they are burned at the mouth of In order toassure that all of the back flowing combustible gases shall be soshortcircuited, I provide a coal seal in the coal tube two conveyors aredriven from a sprocket l3 or other suitable drive, located outside ofthe coal intermediate the coal box and vent, and this leads to aconsideration of the conveyor l2 within the coal tube II. It will beobserved in Figure 2 that this conveyor has a wide pitch in that portionwhich lies adjacent the coal box and in that portion which extends froma point anterior to the vent, to the burner, but that between theseregion's of wide pitch there is a zone a in which the helices of theconveyor have a narrow pitch. The result of this is that while the coalleaving the coal box under the propulsion of that part of the conveyorof wide pitch has a loose and open formation and does not fill the coaltub to the top, it is congested, densified and banked 4 up in the zone aso that it fills the coal tube and acts as a plug or trap to block thepassage of gas through the coal tube toward the coal box. After the coalhas passed through the zone a its forward movement is accelerated by thewide pitch helices In order to localize this region of congestion, the

last helix or so 25 of the conveyor is made of somewhat greater diameterthan the helices that precede it and also of wider pitch. The extremeend 26 of the conveyor is preferably made of noncorroding andwear-resisting steel.

Exclusion of coal dust from the burner is accomplished by the followinginstrumentalities. The coal box 4 which in existing stokers servesmerely as the base for hopper employed as alternative to the bin as acoal supply, in the present invention is closed by a plate 2! convertingthe coal box into a substantially air-tight chamber. The floor of thecoal box has the form of a ramp 28 having a gradual upward incline fromthe adjacent mouth of the coal tube 9 and an abrupt downwardly inclinedside 29 toward the adjacent mouth of the coal tube 1 I. The coal withits accompaniment of dust is delivered from the bin by the conveyor IDto the gradually inclined side of the ramp which it ascends underpressure of the conveyor and then cascades loosely down the abrupt side29. The coal dust released from the larger coal particles goes intosuspension in the atmosphere of the coal box I. The reference character30 indicates the mouth of a suction vent which leads into the combustionchamber 6 near the mouth of the burner 3. Suction may be produced inseveral ways, as will by means of which the atmosphere of the coal box,including the suspended dust, is continuously evacuated through the vent30 and into the combustion chamber 6. The coal freed from the dust ispicked up by the conveyor l2 and delivered to the burner.

It is well known that about two-thirds of the heating efllciency of anyburner is in the form of radiant heat which accompanies incandescence,and the coal dust being in the form of small particles, burnsincandescently in the ignition zone of hot air immediately over themouth of the burner. Inasmuch as the quantity of coal dust may vary indifferent samples of coal, it is desirable to produce an auxiliaryquantity of coal dust so as to ensure continuous lively incandescentcombustion of dust at the mouth of the burner. This I provide by meansof a pulverizer 3| on the shaft 32 of the conveyor 9, Figures 1 and 4show that this pulverizer comprises a deeply ridged drum 33, the ridges34 of which engage the coal particles as the shaft 32 rotates andcrushes them against one another, reducing them all to a substantiallyuniform size, pulverizing some and producing coal dust which isseparated from the coal column with the inherlocalized region where thecoal column is densified and fills the coal tube. To prevent this regionof densiflcation from working forward,

the diameter of the helix immediately preceding the pulverizer is madethe full diameter of the interior of the coal tube, as shown at 38 inFigures, 1 and 2. Another region of densification occurs where the coalis elevated in the coal box 4 up the ramp 28. In order to relieve thepulverizer of the back pressure effects of this region of densification,the terminal helices 39 of the ,fconveyor II] are made with a wide pitchand a diameter substantially equal to that of the interior of the coaltube. The end of the conveyor I0 adjacent the coal box is preferablymade of wear-resistant steel.

The shape of the ramp 2B affords a housing beneath the coal box, intowhich the aligned ends ent dust as the coal cascades over the ramp 28. l

vided with elongated openings 35 and 36, substantially throughout thatportion which reaches into the bin, the sides of said portion beingpreferably closed as shown in Figure 3. The extreme end portion of saidcoal tube remains in the form of an unbroken circle, as shown at 31 inFigure 2. The shaft 32 and the conveyor l0 extend substantially to theend of the coal tube, but the shaft I0 preferably has no bearing in theend of the coal tube. This permits the conveyor to normally lie freelyagainst the lower wall of the coal tube in that portion which extendsinto the bin. The helices of the conveyor, 'at least in this portion ofthe coal tube. are of smaller diameter than the interior of the coaltube, which permits the end portion of the conveyor to flex in variousdirections through the inherent resiliency of the shaft yielding tolocal excess pressure of the coal entrained by the conveyor through theopenings 35 and 36 and 'avoiding jamming of the conveyor and breaking orstalling of the apparatus. This is a very important feature of theinvention, for it will be lunderstood that while the coal .in the binhas been sized at the mine, there will be many lumps not of the propersize which might cause jamming of the conveyor if it were rigidlymounted so as to rotate inflexibly in a prescribed path.

That portion of the conveyor helix which extends into the bin is madewith a relatively close pitch so as to pick up the maximum quantity ofcoal. The pitch widens in the zone b of the conveyor which lies betweenthe bin and the pulverizer -3l, so that the coal mass is loosened anddoes not'iill the conveyor to the top. This promotes easy flow of thecoal toward the pulverizer, reduces the power required to operate thestoker, and minimizes the hazard of the conveyoriamming. The pulverizer3| creates a of the conveyors l0 and I2 extend, said conveyors beingcoupled to the sprocket l3 which is positioned in said housing andprotected from becoming clogged with coal or other debris;

Referring now to the groupof Figures 5, 6, and Y 7, Figure 5-shows thatthe vent 30 which evacuates the coal dust from the coal box 4 into thecombustion chamber 6 is, served by an auxiliary fan 40 blowing into thecombustion chamber 6 and entraining the dust-laden air from the coalbox. I

Figure 6 shows a slightly modified form of the invention in which thechimney draft induces vacuum in the vent 30. I

Figure 7 shows a still further modification of the invention, in whichthe vent 30 opens-into a branch air conduit, debouching from the mainair conduit 2|- and entering into the combustion chamber 6, suction uponthe coal box being produced through the forced draft through the branchconduit 4|.v

Referringnow to Figures 8 and 9, a development of the invention isdisclosed which ine eludes the preheating of the air admitted to theburner 3. Figure 1 shows the stoker I associated with a boiler 42, saidboiler having a com bustion chamber 43 beneath an anterior group ofwater sections 44. The combustion chamber is walled off as at 45 at anintermediate point, leaving certain of the water sections 46 outside ofthe direct heating influence of the burner 3. These water sections areheated by products of combustion which pass upwardly between the watersections of group 44, across the top of the boiler, and down between thewater sections 46, then out through the smoke pipe 41 to a stack 48.

In this form of the invention, the air for supplying the blower 5 comesin through a number of tubes 49 which extend through a portion of thesmoke pipe, as shown, then upwardly through the spaces between thewatersections 46, then across the top of the boiler, then downwardly throughthe space in front of the first water section of the group 44, openinginto a headeril] which forms the end wall of the air conduit leading tothe center of the blower. It will be observed that the air travelscontra-flow to the combustion gases, an arrangement which produces themaximum rate of heat exchange all along the line. The boiler has a coverplate 52 which when removed exposes an opening giving access of a gardenhose by means of which the combustion spaces within the boiler andincluding the outer surfaces of the tubes 49 may be cleaned-*1 An ashpit 53 underlies the boiler in communication with the lower part of thecombustion chamber 43. The rear portion of the ash pit- 53 whichunderlies that portion ofthe boiler which is not in the direct influenceof the burner 31s separated Y from theash pit by a removable plate 54,which plate normally prevents escape of the combustion products into theash pit, and when removed permits the accumulation of fly ash todump'into the ash pit.

Figure 9 shows a slightly modified form of the invention in which theair enters a conduit 55 and passes to the center of the blower outsideof the boiler. A drum 56 is intercalated both in the smoke pipe 41 andin the air conduit 56. This drum has a, core of tubes 51, the oppositeends of which open in headers 58 and 59 and communicate with the smokepipe. The fresh air passes through the drum on the outside of thesetubes and is w armedthrough heat transfer from the combustion gasespassing through said tubes. It is within the purview of the invention toreverse the direction of the tubes and headers, if desired, so as totake the fresh air in through the tubes and have the products ofcombustion pass by the tubes. f"

It will be understood to those skilled in the art that I have in theabove description disclosed what I consider to be a preferred andpractical embodiment of the invention and one which tests have proven tobe more emcient and reliable in operation than stokers as heretoforemanufactured. It will be also understood that the specific details ofconstruction and arrangement of parts as shown and described are by wayof illustration and not to be construed as limiting the scope of theinvention as defined in the appended claims.

What I claim as my invention is:

1. Coal stoker of the underfeed type having a burner comprising a casingdefining a fuel chamber, a blower, a jacket surrounding said casing andin communication with said blower, said casing having air louverscommunicating with the jacket chamber and the fuel chamber, a coal tubeconnected to the lower end of said casing, a helical conveyor in saidcoal tube for feeding coal to said burner having the intermediateportion of its helix of narrower pitch than the extreme portions wherebycondensation-of coal is produced in said portion of narrow pitch forminga gas stop, and a vent from said coal tube into said combustion chamberbetween said burner and gas stop.

2. Coal stoker of the underfeed type having "a burner comprising acasing defining a fuel chamher, a blower, a jacket surrounding saidcasing and in communication with said blower, said casing having airlouvers communicating with the jacket chamber and the fuel chamber,means forming a combustion subject to stack draft, surrounding saidburner, means forming a chamber in which coal dust is separated from thecoal,

. coal feeding means including a coal tube and enclosed helical conveyoradapted to bring coal from a supply source to said separating chamber,

coal feeding means comprising a coal tube from said separating chamberconnected to the lower end of said casing and an enclosed helicalconveyor for moving coal from said separating chamber to said burner,means in said separating chamber interposed between the-adjacent ends ofsaid conveyors comprising a ramp sloping upwardly from said first namedconveyor up which coal is pushed by the first conveyor, terminating inan abruptlydownwardly extending shoulder causing gravitational fall ofcoal from said ramp into the second conveyor, for causing the column ofmoving coal to loosen whereby 16 the dust is'i'reed from the coal sothat it goes into suspension in the atmosphere of said separatingchamber, and means for evacuating the dust-laden atmosphere of saidseparating chamber into the combustion zone in said combus-- tionchamber.

3. Coal stoker of the underfeed type having a burner comprising a casingdefining a fuel chamber, a blower, a jacket surrounding said casingandin communication with said blower, said casing having air louverscommunicating with the jacket chamber and the fuel chamber, meansforming a combustion chamber subject to stack draft, surrounding saidburner, means forming a chamber in which coal dust is separated from thecoal, coal feeding means including a coal tube and enclosed helicalconveyor adapted to bring coal from a supply source to said separatingchamber, coal feeding means comprising a coal tube from said separatingchamber connected to the lower end of said casing and an enclosedhelical conveyor for moving coal from said separating chamber to saidburner, a ramp insaid separating chamber providing an incline facing thefirst named conveyor up which the coal is elevated by said first namedconveyor, said ramp providing an abrupt drop on the side facing thesecond named conveyor permitting the coal to cascade gravitationallytoward the second named conveyor whereby the coal mass is lodsenedfreeing the dust from the coal so that it goes into suspension in theatmosphere of said separating chamber, and means for evacuating thedust-laden atmosphere of said separating chamber into the combustionzone in said combustion chamber.

'4. Coal stoker of the underfeed type having a burner comprising acasing defining a fuel chamber, a blower, a Jacket surrounding saidcasing and in communication; with said blower, said casing having airlouvers communicating with the jacket chamber and the fuel chamber,means forminga combustion chamber subject to stack draft, surroundingsaid burner, means forming a chamber in which coal dust is separatedfrom the coal, coal feeding means including a coal tube and enclosedhelical conveyor adapted to bring coal from a supply source to saidseparating chamber, coal feeding means comprising a coal tube from saidseparating chamber connected to the lower end or said casing and anenclosed helical conveyor for moving coal from said separating chamberto said burner, a ramp in said separating chamber providing an inclinefacing the first named conveyor up which the coal is elevated by saidfirst named conveyor, said ramp roviding an abrupt drop on the sidefacing the second named conveyor permitting the coal to cascadegravitationally toward the second named conveyor whereby the coal massis loosened freeing the dust from the cool so that it goes intosuspension in the atmosphere of said separating chamber, the elevationof coal up said ramp providing gravitational densiflcation of the coalmass at the discharge end of said first named conveyor, restricting airinduction into said separating chamber by way of said first named coaltube, ancl'means for evacuating the dust-laden atmosphere of saidseparating chamber into the'combustlon zone in said combustion chamber.

5. Coal stoker of the-underfoot! type having a burned comprising acasing defining a fuel chamher, a blower, a jacket surrounding saidcasinl ing having air louvers communicating with the jacket chamber and-the fuel chamber, means forming a combustion chamber subject to stackdraft, surrounding said burner, means forming a chamber in which coaldust is separated from the coal, coal feeding means including a coaltube and enclosed helical conveyor adapted to bring coal from a supplysource to said separating chamber, coal feeding means comprising a coaltube from said separating chamber connected to the lower end of saidcasing and an enclosed helical conveyor for moving coal from saidseparating chamber to said burner, a ramp in said separating chamberproviding an incline facing the first named conveyor up which the coalis elevated by said first namedconveyor, said ramp providing an abruptdrop on the side facing the second named conveyor permitting the coal tocascade gravitationally toward the second named conveyor whereby thecoal mass is loosened freeing the dust from the coal so that it goesinto suspension in the atmosphere of said separating chamber, theelevation of coal up said ramp providing gravitational densification ofthe coal mass at the discharge end of said first named conveyor,restricting air induction into said separating chamber by way of saidfirst named coal tube, means for evacuating the dust-laden atmosphere-of said separating chamber into the combustion zone in said combustionchamber, the second named helical conveyor having an intermediateportion of its helix of narrower pitch than the extreme portions,whereby densification of coal is produced in said portion of narrowpitch forming a gas stop, and a vent from said coal tube to saidcombustion chamber between said burner and gas stop.

6. Coal stoker of the underfeed type having a bring coal from a supplysource to said separating chamber, coal feeding means comprising a coaltube from said separating chamber connected to the lower end of saidcasing and an enclosed helical conveyor for moving coal from saidseparating chamber to said burner, means in said separating chamberinterposed between the adjacent ends of said conveyors for causing thecolumn of moving coal to loosen whereby the dust is freed from the coalso that it goes into in communication with said blower,said casinghavingair louvers communicating with the jacket chamber and the fuel chamber,means forming a combustion chamber subject to stack draft, surroundingsaid burner, means forming a chamber in which coal dust is separatedfrom the coal,

coal feeding means including a coal tube and enclosed conveyorcomprising a shaft and helical vane adapted to bring coal from a supplysource to said separating chamber, coal feeding means comprising a coaltube from said separating chamber connected to the lower end of saidcasing and an enclosed helical conveyor for moving coal from saidseparating chamber to said burner, a ramp in said separating chamberinterposed between adjacent ends of said conveyors presenting an inclineto the end of the first named conveyor for causing the column .of movingcoal to be elevated up said ramp and having an abrupt drop facing theend of the second named conveyor causing the coal to cascadegravitationally whereby its mass is loosened and dust freed from thecoal which goes into suspension in the atmosphere of said separatingchamber, a pulverizer interposed on the shaft of said first namedconveyor for sizing the coal and producing coal dust, and means forevacuating the dust-laden atmosphere of said separating chamber into thecombustion zone in said combustion chamber.

8. Coal stoker of the underfeed type having a burner comprising a casingdefining a fuel chamber, a blower, a jacket surrounding said casing andin communication with said blower, said casing having air louverscommunicating with the jacket chamber and the fuel chamber, meansforming a combustion chamber subject to stack draft, surrounding saidburner, means forming a chamber in which coal dust is separated from thecoal, coal feeding means including a coal tube and enclosed helicalconveyor adapted to bring coal from a supply sourc to said separatingchamber, coal feeding means comprising a coal tube from said separatingchamber connected to the lower end of said casing and an enclosedhelical conveyor for moving coal from said separating chamber to saidburner, means in said separating chamber interposed between the adjacentends of said conveyor for causing the column of moving coal to loosenwhereby the dust is freed from the coal so that it goes into suspensionin the atmosphere of said separating chamber, and means for evacuatingthe dustladen atmosphere of said separating chamber into the combustionzone in said combustion chamber, said means including an eductionconduit from said separating chamber opening into said combustionchamberin th active combustiorr zone thereof and subject to stack draft.

9. Coal stoker of the underfeed type having a burner comprising a casingdefining a fuel chamber, a blower, a jacket surrounding said casing andin communication with said blower, said casing having air louverscommunicating with the jacket chamber and the fuel chamber, meansforming a combustion chamber subject to stack draft, surrounding saidburner, means forming a chamber in which coal dust is separated'from thecoal, coal feeding means including a coal tube and enclosed helicalconveyor adapted to bring coal from a supply source to said separatingchamber, coal feeding means comprising a coal tube from said separatingchamber connected to the lower end of said casing and an enclosedhelical conveyor for moving coal from said separating chamber to saidburner, means in said separating chamber interposed between the adjacentends of said conveyor for causing the column of moving coal to loosenwhereby the dust is freed from the coal so that it'goes into suspensionin the atmosphere of said separating chamber, and means for evacuatingthe dustlation to said auxiliary blower conduit;

10. Coal stoker of the underfeed type having a burner comprising acasing defining a fuel chamber, a blower, a jacket surrounding saidcasing and in communication with said blower, .said casing having airlouvers communicatingwith the jacket chamber and the fuel chamber, meansforming a combustion chamber subject to stack' draft, surrounding saidburner, means forming a chamber in which coal dust is separated from thecoal, coal feeding means including a coal tube and enclosed helicalconveyor adapted to bring coal from a supply source to said separatingchamber, coal feeding means comprising a coal tube from said separatingchamber connected to the lower end of said casing and an enclosedhelical conveyor for moving coal from said separating chamber to saidburner, means in said separating'chamber interposed between the adjacentends of said conveyor for causing the column ofmoving coal to. loosenwhereby the dust is freed from the coal so that it goes into 'suspensionin the atmosphere of said separating chamber, and means for evacuatingthe dustladen atmosphere of said separating chamber into the comlmstlonzone in said combustion chamber, said means including a branch conduitfrom said blower opening into said combustion chamber in the activecombustion zone thereof and subject to stack draft, and an eductionconduit from said separating chamber in air-entraining relation to saidbranch conduit.

'JAMES A. CASEY.

